correct job name and use faster luacheck action

.github/workflows/luacheck.yml

@@ -1,13 +1,10 @@
 name: luacheck
 on: [push, pull_request]
 jobs:
-  build:
+  luacheck:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
-    - name: apt
-      run: sudo apt-get install -y luarocks
-    - name: luacheck install
-      run: luarocks install --local luacheck
-    - name: luacheck run
-      run: $HOME/.luarocks/bin/luacheck ./
+      - name: Checkout
+        uses: actions/checkout@master
+      - name: Luacheck
+        uses: lunarmodules/luacheck@master